1. Field of the Invention
The present invention generally relates to a lighting apparatus, and especially relates to a lighting apparatus that has a luminous layer inserted between two electrode layers.
2. Description of the Related Art
Devices that are equipped with displays on both sides of an opening-and-closing (folding-and-unfolding) section, such as a folding type cellular phone, are widely used. With such devices, users can view some information regardless of the opening-and-closing state of the section. Such devices often use a liquid crystal display (LCD) for displaying. Since the LCD does not emit light by themselves, a back light or front light, which is an internal light source, is required in order to make visible the information to be displayed. As the internal light source, a layer of electroluminescent (EL) material can be used. When preparing the displays on both sides of the opening-and-closing section, one straightforward configuration is separate LCD and separate internal light sources for each of the sides. According to this configuration, two sets of displays, each consisting of an LCD and an internal light source, are provided, one on the front side and the other on the rear side.
However, this configuration is disadvantageous in view of increased thickness of the display. This is because it is necessary to provide a certain distance between the two sides in order to prevent the display on one side from interfering with the display on the other side. Especially in the case of portable devices that are required to be small and thin, increase in the thickness is especially a disadvantage. An example of solving this problem is shown in FIG. 1, wherein the two sides share one internal light source. According to the example shown in FIG. 1, a luminous layer is sandwiched by a surface electrode layer and a back electrode layer, each being covered by an insulation layer. Here, the single luminous layer serves two displays, and thickness, weight, etc., are reduced accordingly.
[Patent Reference 1] JPA 2001-35652
Problem(s) to be Solved by the Invention
Here, it is often the case that dimensions of the two displays are different. That is, one side (main display) has a greater area than the other side (sub-display). If the single luminous layer is shared by the front and rear displays, the luminous layer provides the same light volume to both displays, regardless of the size difference. Accordingly, when information is displayed only on the sub-display, the luminous layer provides a light volume beyond necessity, which is a problem in that it uselessly consumes energy. Since it is important for the portable devices to save power, the problem is highly disadvantageous. The problem is not only with a display using an EL layer but also with other displays that use a back light (the light source being light emitting diodes (LED), a cold-cathode fluorescent lamp (CCFL), etc.), wherein the light is uniformly distributed from the light source by an optical guide plate for the greater display area. That is, when only a smaller area is used for display, the use efficiency of the light is degraded.